Voltage in a power system, unlike frequency, is regarded as a local problem. Accordingly, in order to maintain only the voltages of substations within a predetermined range, individual voltage compensators (e.g., a capacitor, a reactor, a Flexible AC transmission system (FACTS), etc.) are installed and operated in each substation.
An operating scheme using such a voltage compensator is effective from the standpoint of the maintenance of voltage for each substation, but is inefficiently operated at present because reactive power sources installed near the substation to maintain the voltage quality of the entire system are not taken into consideration.
Further, with the rapid development of Information Technology (IT) and high-speed computing technology, technologies for managing the voltage quality of the entire system via a Voltage Management System (hereinafter referred to as “VMS”) have recently been developed. For example, the VMS divides the entire power system into a plurality of electrically isolated voltage control areas so as to manage voltage quality using voltage control. The VMS selects a representative substation of each voltage control area. The VMS cooperatively controls reactive power sources (e.g., power generators, capacitors, reactors, FACTS, etc.) installed in local systems so that the voltage of the selected representative substation is maintained at a uniform level (e.g., 1.0 per unit (p.u.)).
Such a VMS is configured to control the voltage of a power transmission substation (of 154 kV or more) and is operated in such a way that it is mounted on a central energy management system (hereinafter referred to as “EMS”) or configured as a separate device. The EMS processes a 22.9 kV or less power distribution system as a load, and performs energy management via the Automatic Tap Changer (Automatic Voltage Regulator: AVR) of a transformer without including the power distribution system in an operation target. Here, an AVR is operated separately from the EMS and is configured to maintain a secondary side voltage of a 154 kV/22.9 kV transformer within a predetermined range.
In a power distribution system, various distributed power sources or microgrids (MGs) have become more popular and extensive and loop operations are made possible. Accordingly, a Distribution Management System (hereinafter referred to as “DMS”) that will manage a complicated power distribution system, as in the case of the EMS of a power transmission system, has been developed.
As shown in FIG. 1, a current power grid 10 is connected to a plurality of loads 20 and a plurality of power generators 30 (e.g., distributed power sources, etc.). That is, the power grid 10 is additionally connected to distributed power sources such as wind power, photovoltaic, and tidal energy storage devices, and fuel cells.
Meanwhile, as shown in FIG. 2, in the power grid, an EMS 40 (or VMS) and a DMS 50 are installed and operated for the overall operation of a power system, including the maintenance of voltage quality of the power grid. That is, the EMS or VMS is connected to a power transmission system to maintain the voltage quality of the power transmission system, and the DMS is connected to a power distribution system to maintain the voltage quality of the power distribution system.
Here, as shown in FIG. 3, in the power transmission system, the EMS maintains the voltage quality of the power transmission system by performing voltage control based on respective voltage compensators installed in power transmission substations. Of course, as shown in FIG. 4, a voltage control scheme using the VMS may also be used instead of the voltage control scheme using voltage compensators.
Voltage control in the power transmission system using an EMS (or VMS) or voltage control in the power distribution system using a DMS is independently performed. However, the power transmission system and the power distribution system are connected to each other via a 154 kV/22.9 kV transformer, and thus the power transmission system may sufficiently utilize energy resources connected to the power distribution system if necessary.
The voltage of the power transmission system is suitably controlled for the purpose of maximally securing a dynamic reactive power reserve within the system so as to prevent a wide area power failure caused by voltage instability in the case of an accident from occurring by means of the EMS (or VMS).
In particular, when a power system is in a no, mat state without causing accidents (that is, a sufficient reactive power reserve is present in the system), it may be considered that the role of the EMS or DMS is desirably performed merely by maintaining its own individual function without mutual cooperative control. In contrast, in the case of an accident causing voltage instability (that is, when a reactive power reserve is inefficient), there is a problem in that it is impossible to compensate for reactive power by efficiently utilizing the resources of the system via cooperative control of the EMS and the DMS.
Meanwhile, the DMS connected to the power distribution system takes charge of complicated operation of the power distribution system including voltage control thereof. That is, the DMS cooperatively controls various distributed power sources and various voltage compensators connected to the power distribution system, thus maintaining the voltage of the power distribution system within the range of predetermined voltages.
Recently, as the number of various distributed power sources and reactive power compensators connected to the power distribution system has increased, a cooperative control regulation device for efficiently utilizing added resources (e.g., distributed power sources and reactive power compensators) is required. For example, Korean Patent Application Publication No. 10-2010-0047726 (entitled “Optimized Voltage control methodology through coordinated control of reactive power sources”) discloses technology for performing cooperative control of reactive power sources using a variation in reactive power. Korean Patent No. 10-1039425 (entitled “System and method for controlling voltage of electric power system”) discloses technology for performing cooperative control of reactive power sources using reactive power margin of the reactive power sources.
However, a problem arises in that, in the past, the power transmission system and the power distribution system perform cooperative control in consideration of only reactive power sources in each system, thus making it impossible to efficiently maintain the voltage quality of the entire power system, and making it difficult to cope with an increase in the number of reactive power sources.